Since these spells require Chaos Runes, they are more expensive, but this is still a relatively cheap way of training Magic. On reaching level 17 Magic you should switch to Wind Bolt and then proceed through the Bolt spells as you unlock them.
You can mitigate the additional rune requirements of these elemental Strike spells by equipping a corresponding elemental staff.
When you unlock Water Strike, Earth Strike, or Fire Strike, you should switch to those for faster Magic training.
